The present invention relates to the field of rolls of tissue paper or other, similar, material such as nonwovens. It relates in particular to the field of products for sanitary and/or domestic use such as, for example, rolls of wiping paper, paper towelling or bathroom tissue.
The term “tissue paper” should be understood to mean a paper with characteristics as defined by the European standard EN 12625-1.
A roll is formed by winding a continuous sheet which consists of one or more plies of paper. The sheet is possibly pre-cut into consecutive segments in the winding direction, and is wound, preferably, about an axis or a spindle that may or may not support a core; the roll can thus comprise a central core or not.
According to the applications, the roll is unwound, either from its outer surface in the direction of winding perpendicularly to its axis, in which case the unwinding is said to be tangential, or via the interior, from the centre in its axial direction. In the latter case, the roll is said to be centrally unwound.
The present invention relates to rolls, that have a central hole, centrally unwound, and rolls with tangential unwinding.
When the roll is intended for an application of the type with central unwinding, it can include a core. The core is a cylinder of cardboard that extends over the width of the roll. It generally comprises a strip of cardboard wound in a helical spiral. In this case, it is essential to begin by extracting the latter when putting the roll to use. For example, the core can be designed so as to be able to be torn when pulled on its edge at one end of the helical spiral of cardboard of which it is formed. However, practice shows that this solution is not always satisfactory, because extracting the core can sometimes prove difficult if the rupture area or areas are malformed. Furthermore, the first sheets of the roll may be dragged out, making them difficult to use. The first turns of the sheet are more often than not glued to the core, so they are unfit for any use and constitute waste.
This type of core is costly to produce, since it generally consists of two or more layers of cardboard bonded by gluing and is associated with glue for “attaching” the first turn of the roll. It is also useless once removed, and therefore becomes waste.
To overcome this drawback, there have also been proposed, according to the prior art, rolls with central unwinding but coreless. These are a priori easier to implement by the user, because there is no longer a need to remove a core before putting them to use. To produce them, it is possible, during manufacture, to provide a provisional core forming a spindle onto which the sheet is wound. The spindle is then removed, before the rolls are packaged. This technique presents constraints on the industrial level, because a station for extracting the spindles must be added to the winding line.
According to a known method of manufacture without core, the sheet is cut in line in the running direction of the latter or longitudinally, before winding on the spindle, from a very wide mother sheet, into as many strips as there are individual rolls to be obtained.
According to another method of manufacture, the mother sheet is wound directly onto a spindle, also without the insertion of a core. The initial sheet which is very wide, is first wound in such a way as to form a single reel with the final diameter of the individual roll, called “log” in the field. When formed, the log is extracted from the spindle and it is cut into individual rolls.
However, the sheet, whether it be of tissue, creped dry or wet, dry-laid paper or a nonwoven, has a certain elasticity. Because of the internal stresses of the roll, due, for example, to the clamping of the sheet onto the spindle during winding, and/or to the tension of the sheet generated by the machine unwinding/winding operation, it is normally not possible to avoid reduction of the diameter of the central hole by sagging or collapse at the centre of the first turns after the spindle has been removed. This collapse is produced, for example, after extraction of the spindle or when the log is cut, by the pressure exerted by the saw or even in packaging and overpackaging operations.
A partial or total reduction of the central hole is observed during handling and transportation operations, because of the inevitable vibrations and pressures to which the rolls are subjected.
When the central hole is completely reduced, it is difficult to reform it by hand, and it is no longer easy to grasp the first turn. Waste is inevitably produced, in particular when the roll is put to use in a dispenser, because it is then necessary to grasp several turns at a time.
Also known are coreless rolls, the central hole of which remains formed after extraction of the spindle and/or after cutting by a saw. It is possible, for example, to use a spindle with a splined or polygonal-section profile to form a central hole, the walls of which are self-supporting. One exemplary embodiment is illustrated by patent FR 2 554 799.
If the central hole is of small diameter, the first turns remain difficult to access. The leader takes the form of a tight bundle, helical with small pitch, that does not lend itself to easy extraction.
If the diameter of the central hole is larger, the first turns must be joined together. For this, a bonding agent is applied that is deposited directly onto the sheet or indirectly via the spindle onto the winding cylinders, by an appropriate system, when the first turns are wound onto the spindle. Any other principle of joining the first turns together, by a mechanical method in particular, can be applied. These first turns are thus consolidated, and together they withstand the forces of the internal stresses.
However, once again, waste cannot be avoided when putting such a roll to use. Whether in the case of a direct use or in the case where this roll were to be used in a dispenser with central unwinding in which the end of the sheet must be inserted into a relatively narrow dispensing orifice, the first turns joined together must first be eliminated.
In the latter type of embodiment, it is impossible to avoid, for certain rolls, the sagging of the central hole, as in the cases mentioned above, because of impacts in transportation. To avoid this risk, provision is also made to preferably package the rolls in cardboard cases, unlike the rolls with core for which a flexible jacket of paper or plastic material is sufficient. The cost is thereby increased.
The benefit that could be obtained from these coreless rolls compared to the rolls with core is thus diminished.
The applicant has developed a coreless roll, said to be with central unwinding, comprising an unwinding leader that is central in relation to its axis, designed to facilitate the grasping of the innermost turns of the roll. This technique is described in the patent applications FR 2 869 891 and EP 1 636 123. It is a specific solution to the problem of collapse of the central hole of coreless rolls.
The present invention provides a different and inventive solution to this same problem and is applicable not only to rolls said to be with central unwinding, but also to rolls with tangential unwinding.